Unit Auxillary Transformer of 210 MW of Thermal Power Plant

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           The unit switchgear is charged from incomer from unit auxiliary transformer when machine is on bar and station switch gear is charged from incomer from station transformer.

                The unit switchgear is provided with tie from station switchgear and the station switchgear provided with tie from station switchgear of other unit. Normally, the station switchgear is charged from concern station incomer.

Taking incomer from UAT in service

  • Incomer breaker should be rack in service position.
  • DC supply made “ON”
  • All relay on incomer breaker should be reset condition.
  • Connect the synchronous trolley.
  • Put the UAT incomer synchronous switch in “ON”
  • Put the trip selection switch on tie breaker on control panel in control room.
  • The incomer breaker should be made “ON” when green lamp on synchronizing trolley glows green.
  • Tie breaker should trip on auto after closing of incomer breaker.

Taking tie breaker in service

  • Tie breaker should be rack in service position.
  • DC supply made “ON”
  • All relay on tie breaker should be in reset condition.
  • Connect the synchronous trolley.
  • Put the trip selection switch in control room on incomer breaker.
  • Put Auto /manual switch of tie breaker on manual position.
  • The tie breaker should be made “ON” when green lamp on synchronizing trolley glows green. The incomer breaker should trip on auto after closing of the tie breaker.

Note: The incomer / tie breaker trips on Auto only when respective unit station incomer breaker is  in ON position. Trip the incomer / tie breaker manual 

For taking in service the tie breaker when the unit bus is dead, put the incomer breaker of respective unit in service position ( create service position ).

Isolation of UAT incomer breaker.

  • Confirm that the tie breaker in service position.
  • Connect the synchronous trolley.
  • Put the trip selection switch in ON incomer breaker in control room.
  • Put Auto / manual switch of tie breaker on manual position.
  • The tie breaker should be made “ON” when green lamp on synchronizing trolley glows green.
  • The incomer breaker should trip on auto after closing of the tie breaker
  • DC supply of incomer breaker made OFF.
  • Rack out the incomer breaker in test position.
  • Remove the breaker plug.

Never take trial of incomer breaker in test position.

STATION SWITCHGEAR.

 There are two station transformer provided in unit no 3 and 4. There are total four breakers for station incomer and tie to station switchgear.

1. Incomer from station incomer from unit no 3 on bus SS IIA

2. Incomer from station incomer from unit no 4 on bus SS IIB

3. Tie to SSIIA to SS II B ( unit no 3 to unit no 4 ) on  SS IIA bus.

4. Tie to SSIIB to SS II A ( unit no 4 to unit no 3 ) on  SS IIB bus.

 Taking incomer breaker in service.

  • Incomer breaker should be rack in service position.
  • DC supply made “ON”
  • All relay on incomer breaker should be reset condition.
  • Confirm that the 220 KV side breaker is in ON position.
  • Check the voltage of incomer breaker at 6.6 KV control room
  • Connect the synchronous trolley.
  • Put the incomer synchronous switch in “ON”
  • Put the trip selection switch on the breaker which is required to be for isolation in control room.
  • The incomer breaker should be made on when green lamp on synchronizing trolley glows green.
  • The required breaker should trip on auto after closing of incomer breaker.

Closing of TIE Breaker.

  • Tie breaker should be rack in service position.
  • DC supply made “ON”.
  • All relay on tie breaker should be reset condition.
  • Connect the synchronous trolley.
  • Put the tie synchronous switch in “ON”
  • Put the trip selection switch on the breaker which is to be required for isolation in control room.
  • The tie breaker should be made on when green lamp on synchronizing trolley glows green,
  • The required breaker should trip on auto after closing of tie breaker.

There are main six  415 volt buses in each unit which are as follows.

  1. Unit service switchgear.
  2. Station service switchgear.
  3. Boiler MCC.
  4. Turbine MCC.
  5. Emergency bus
  6. Miscellaneous MCC.

The unit service switchgear is charged from unit service transformer of each unit. From unit service switchgear the supply goes to Boiler MCC and turbine MCC. Similarly station service switch gear is charged form station transformer. The supply from station switchgear goes to boiler MCC, turbine MCC and emergency bus. 415 V tie has been provided between station switchgear and unit switchgear also. Over and above tie has been provided between station service switchgear, SSS IIA to station service Switchgear SSS II B.

Boiler MCC/Turbine MCC

The Boiler MCC/ Turbine MCC is used to provide supply to boiler/turbine side main auxiliary. There is incomer from station switchgear and unit switchgear. One side of MCC is charged form station switchgear and other side is charged from unit service transformer. Between incomer, there is bus coupler. If any of incomer OFF due to under voltage the bus coupler will come on auto.

Taking incomer Breaker of TMCC / BMCC in service

  • Rack in the incomer breaker.
  • DC supply made “ON”.
  • All relay on panel should be in reset condition.
  • Check both side phase voltage for grounding ( If grounding found then don’t take incomer breaker.)
  • Take incomer breaker manually from 6.6 KV control room.
  • The bus coupler breaker trips on Auto after closing of incomer breaker.

Miscellaneous MCC

The Miscellaneous MCC is charged from Miscellaneous MCC form respective unit. Tie has been provided between Miscellaneous MCC of unit no 3 to unit no 4.

Taking incomer in service

  • Rack in the incomer breaker.
  • DC supply made “ON”.
  • All relay on panel should be in reset condition.
  • Check both side phase voltage for grounding ( If grounding found then don’t take incomer breaker.)
  • Take incomer breaker manually from 6.6 KV control room.
  • The tie breaker of unit no 3 trips on Auto after closing of incomer breaker

Note: the tie breaker of Miscellaneous MCC of unit no 4 should be always kept ON. ( Dummy Breaker)

Taking incomer from unit service Transformer in service

  • Put incomer breaker in service position.
  • DC supply made “ON”.
  • All relay on panel should be in reset position.
  • Connect the synchronous trolley.
  • Put synchronous switch of UST incomer in on position.
  • Put the trip selection switch in control room on tie breaker.
  • The incomer breaker should be made on when green lamp on synchronizing trolley glows green.
  • The tie breaker should trip on auto after closing of the incomer breaker.

Taking bus coupler between station service switchgear (SSS) to unit service switchgear (USS)

  • Rack in bus coupler breaker in service position.
  • DC supply made “ON”.
  • All relay on panel should be in reset position.
  • Connect the synchronous trolley.
  • Put synchronous switch of bus coupler in on position.
  • Put the trip selection switch in control room on incomer USS incomer breaker.
  • Put the bus coupler   auto manual switch in manual position in control room.
  • The bus coupler   breaker should be made on when green lamp on synchronizing trolley glows green,
  • The incomer breaker should trip on auto after closing of the bus coupler   breaker.

Taking incomer from Station service transformer

  • Incomer breaker should be rack in service position.
  • DC supply made “ON”
  • All relay on incomer breaker should be reset condition.
  • Confirm that the 6.6 KV side breaker is in ON position.
  • Check the voltage of incomer breaker at 6.6 KV control room
  • Connect the synchronous trolley.
  • Put the incomer synchronous switch in “ON”
  • Put the trip selection switch in control room on the breaker which is to be required for isolation.
  • The incomer breaker should be made on when green lamp on synchronizing trolley glows green.
  • The required breaker should trip on auto after closing of incomer breaker.

Closing of TIE Breaker.

  • Tie breaker should be rack in service position.
  • DC supply made “ON”.
  • All relay on tie breaker should be reset condition.
  • Connect the synchronous trolley.
  • Put the tie synchronous switch in “ON”.
  • Put the trip selection switch in control room on the breaker which is to be required for isolation.
  • The tie breaker should be made on when green lamp on synchronizing trolley glows green,
  • The required breaker should trip on auto after closing of tie breaker.

PRE-START CHECKS.

  • Access to circuit breaker satisfactory.
  • Permanent and adequate lighting of switchgear room is satisfactory.
  • Circuit breaker properly positioned in cubical.
  • Lubrication / greasing of all moving parts satisfactory.
  • Operation of shutter assembly satisfactory.
  • Space heater provided and in service.
  • Earthing complete and satisfactory.
  • Ensure that circuit breaker contact alignment is correct.
  • Circuit breaker position indication working satisfactory.
  • Ensure that there is no sign of pitting etc on contact.
  • Spring charge position indicator working satisfactory.
  • Check that operation of circuit breaker auxiliary contact is alright.
  • Tightness of all connection is satisfactory.
  • Ensure circuit breaker rack out rack in mechanical is working satisfactory.
  • Check for healthiness of Dc control supply. With proper polarity.
  • Check for auxiliary contact for spring charging mechanism working satisfactory.
  • Check for indication lamp provided with proper nomenclature.
  • Measure IR of control circuit / spring charge motor / auxiliary contact / sliding contact.
  • Measure IR for Phase to phase fixed contact in breaker open condition, Moving contact in breaker open condition.
  • Measure breaker spring breaking time in second, Measure breaker spring closing time in second.
  • Check that air gap between moving and fix contact for all phases.
  • Ensure all three poles of breaker closing simultaneously.
  • Measure contact resistance.

CURRENT TRANSFORMER

  • Ensure for correct polarity marking.
  • Ensure correct connection of Current transformer.
  • Check the tightness of connection is OK.

PROTECTIVE RELAYS.

  • Ensure all mounted relays are in good condition working satisfactory.

BREAKER OPERATION.

 ( A ) Breaker in rack out  / test position, check following operation.

  • Manual tripping.
  • Electrical closing.
  • Electrical tripping.
  • Mechanical trip free operation.
  • Electrical trip free operation.
  • Anti pumping operation.

( B ) breaker in rack in position, check following operation.

  • Local electrical closing.
  • Local electrical tripping.
  • Local tripping of switchgear by actuating interlock / protection.
  • Remote electrical closing.
  • Remote electrical tripping.
  • Remote tripping of switchgear by actuating interlock / protection.

( C ) Apply reduce control voltage, 50% of rated value and check following operation.

  • Electrical closing.
  • Electrical tripping.

( D ) protection and interlock circuits.

  • Check the protection and interlock circuits for protection / alarm / setting / trip.

(  E ) Under voltage tripping.

  • Ensure for satisfactory operation of breaker in under voltage condition.

( F ) Ensure for satisfactory operation of auto change over system, if provided